(ANSA-AFP) - BUDAPEST, SEP 30 - Hungary's first ever opposition primary election to find a candidate to challenge Prime Minister Viktor Orban next year was set for a run-off after the first round proved inconclusive, partial results showed on Thursday. Klara Dobrev, 49, an MEP from the leftist Democratic Coalition was first choice of voters among six disparate opposition parties that have united in a bid to topple Orban after 10 years in power they say have been marked by corruption and creeping authoritarianism. But with votes counted in 75 of the 106 electoral districts Dobrev looked to fall short of the outright majority needed to win without a second-round run-off, with 34 percent of ballots cast. The six parties overcame their differences in a bid to find the strongest candidate to oust Orban, 58, in April's elections in what analysts predict will be a close race. Budapest Mayor Gergely Karacsony, 46, a mild-mannered liberal, trailed Dobrev in second place with around 28 percent. (ANSA-AFP).